This invention relates to a control strategy for separately excited DC motors which provides for maximum motor efficiency irrespective of motor speed or loading, and more particularly to a method and apparatus for implementing this strategy.
It is desirable to operate DC motors at maximum efficiency because inefficient DC motor operation results in increased power consumption and motor wear. Operating a DC motor at maximum efficiency is most important when such motor is utilized to provide propulsion for an electric vehicle because the increased power consumption resulting from inefficient motor operation reduces the maximum vehicle range. Additionally, more frequent charging of the vehicle batteries is required for the vehicle to traverse a given distance, causing increased battery drain and, ultimately, a reduced battery lifetime.
Heretofore, conventional DC motor control strategy has not sought to maximize motor efficiency. Rather, maximization of torque/ampere has been a common objective. Use of such a conventional control strategy for a DC motor drive system results in maximum motor efficiency at only one value of motor torque and speed. At other torque values, the DC motor drive system operates inefficiently.
The present invention concerns a control strategy for operating a DC motor drive system at maximum efficiency irrespective of motor loading and speed.